Patent Application
20050145378
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Applications No. 2002-212987 filed on Jul. 22, 2002 and No. 2003-145079 filed on May 22, 2003 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to such a hydrogen-storage container or such a method of occluding hydrogen as makes it possible to significantly enhance a storage amount of hydrogen in comparison with the related art.
2. Description of the Related Art
Hydrogen, which does not generate carbon dioxide through combustion, has been drawing attention as clean fuel. Studies on storage, conveyance, and the like of hydrogen have for long been conducted. As a method of storing and conveying hydrogen, high-pressure gas cylinders are generally employed. However, gas cylinders are heavy, demonstrate a practically limited storage capacity per unit volume, and hence have little prospect of substantial enhancement of hydrogen-storage efficiency. It is to be noted in the present specification that hydrogen-storage efficiency refers to a storage amount of hydrogen per unit internal volume of a hydrogen-storage container.
As a method of storing hydrogen with a high hydrogen-storage capacity per unit volume, it has been known to use hydrogen-occlusion alloy. Hydrogen-occlusion alloy is known to be able to store hydrogen more or less at a normal pressure and to store hydrogen with its volume having been reduced to a thousandth of a volume at a normal temperature and a normal pressure. Taking advantage of this feature, hydrogen-occlusion alloy has been employed as a hydrogen-occlusion material for storing and conveying hydrogen more or less at a normal pressure.
Hydrogen-occlusion alloy is known to undergo a major voluminal change through occlusion of hydrogen, more specifically, to expand cubically by approximately 30% through occlusion of hydrogen. In addition, hydrogen-occlusion alloy employed as a hydrogen-storage material is generally available in the form of powder so as to guarantee an enlarged surface area. Even if a hydrogen-occlusion alloy with large particle sizes is used at the outset, it eventually turns into powder due to its expansion and contraction resulting respectively from occlusion and discharge of hydrogen. When the hydrogen-occlusion alloy as powder expands in a hydrogen-storage container during occlusion of hydrogen, the powder lacks fluidity and has little mobility. Thus, a high pressure is applied to some parts of the container, which faces the danger of being destroyed. In consideration of voluminal expansion of hydrogen-occlusion alloy, therefore, a hydrogen-storage container holding hydrogen-occlusion alloy as a hydrogen-occlusion material according to the related art requires the existence of an internal space (hereinafter referred to as an “air gap portion”) which is not filled with the hydrogen-occlusion alloy. Besides, with a view to preventing a high pressure from being applied partially to the container owing to the lack of mobility of the hydrogen-occlusion alloy as powder at the time of voluminal expansion, the required volume of the air gap portion is actually much larger than a volume that is determined simply by taking expansion of hydrogen-occlusion alloy into account. Namely, in general, no more than about 40 to 60% of the internal volume of the hydrogen-storage container can be filled with hydrogen-occlusion alloy. The remaining space, that is, about 60 to 40% of the internal volume of the hydrogen-storage container must be left as the air gap portion. Those skilled in the art have regarded this air gap portion as a space useless for storage of hydrogen and as one of the reasons why the hydrogen-storage density in the hydrogen-storage container cannot be enhanced. It is to be noted in the present specification that the volume of hydrogen-occlusion alloy is based not on bulk density but on true density.
In order to solve the problem stated above, for example, Japanese Published Patent Official Gazette No. 63-10081 discloses a method of efficiently storing and transporting hydrogen. In this method, a hydrogen-storage container is filled with a hydrogen-occlusion alloy in which hydrogen has been occluded in advance, and the ratio of a volume of an air gap portion to an internal volume of the container is thereby reduced significantly. Although this method makes it possible to increase a storage amount of hydrogen per unit internal volume of the hydrogen-storage container, the hydrogen-storage container increases in weight due to an increase in mass resulting from an increase in amount of the hydrogen-occlusion alloy with which the container is to be filled. Therefore, this method is not absolutely suited to be adopted in fields requiring reduction in weight, for example, to be installed in an automobile.
Further, Japanese Patent Application Laid-Open No. 2002-221298 discloses a hydrogen-storage unit comprising a high-pressure hydrogen-storage tank in which hydrogen is stored in a high-pressure gaseous state, in addition to hydrogen storage means in which a hydrogen-occlusion alloy is accommodated. The hydrogen storage means disclosed in this related art, in which the hydrogen-occlusion alloy is accommodated, can store hydrogen at a maximum pressure of 3 MPa to 5 MPa. According to this related art, however, even if the hydrogen storage means in which the hydrogen-occlusion alloy is accommodated has been increased in pressure, the storable amount of hydrogen does not increase to the extent of matching the increase in pressure. As a counterproductive consequence, the hydrogen storage means increases in weight because of the necessity to ensure pressure resistance. Also, a requirement for sufficient pressure resistance leads to an increase in thickness of walls of a container constituting the hydrogen storage means. This increase in thickness makes it difficult to transfer heat into the hydrogen storage means from the outside. Thus, it takes a long time to supply or store hydrogen. Alternatively, the amount of hydrogen that can be supplied or stored decreases. Still further, the hydrogen storage means is made of aluminum, which is higher in pressure resistance and heat conductivity than resin.
That is, according to the related art based on the following first to fifth standpoints, hydrogen gas, which is at a pressure equal to or somewhat higher than a plateau equilibrium pressure of hydrogen gas contained in a hydrogen-occlusion alloy at a hydrogen-occlusion temperature, is introduced into a hydrogen-storage container made of aluminum so as to be occluded into the hydrogen-occlusion alloy. The first standpoint is that it is desirable to handle high-pressure gas in a hydrogen-storage container employing a hydrogen-occlusion alloy. The second standpoint is that even if the hydrogen-storage container has been filled with hydrogen whose pressure is above a plateau equilibrium pressure, the amount of hydrogen to be stored into the hydrogen-occlusion alloy does not increase significantly. The third standpoint is that an increase in pressure of the hydrogen storage means in which the hydrogen-occlusion alloy is accommodated leads to an increase in weight of the hydrogen storage means because of the necessity to ensure pressure resistance. The fourth standpoint is that a requirement for sufficient pressure resistance leads to an increase in thickness of the walls of the container constituting the hydrogen storage means, that this increase in thickness makes it difficult to transfer heat into the heat storage means from the outside, and that an increase in the time required for filling the container with hydrogen or a decrease in the storable amount of hydrogen is thereby caused. The fifth standpoint is that the hydrogen storage means is preferably made of aluminum, which is higher in pressure resistance and heat conductivity than resin.
Hence, there is a limit imposed on previously known methods of storing hydrogen by means of a hydrogen-occlusion alloy or previously known hydrogen-storage containers employing a hydrogen-occlusion alloy. That is, some of them are designed to store and transport hydrogen with its pressure being held equal to or below a plateau equilibrium pressure of hydrogen gas contained in a hydrogen-occlusion alloy, while being tuned such that the plateau equilibrium pressure is confined to a range of 0 MPa to 1 MPa (a gauge pressure) at a normal pressure, for the purpose of preventing hydrogen from being stored at a high pressure. The others are designed to store hydrogen in a hydrogen-storage container made of an aluminum alloy at a pressure slightly higher than a plateau pressure. This is based on the concepts of making the most of the characteristic of a hydrogen-occlusion alloy, namely, its ability to occlude hydrogen even around a normal pressure, avoiding the necessity to handle the hydrogen-storage container as a high-pressure container, and exploiting heat conductivity of metals such as aluminum alloys.
It is an object of the invention to provide a hydrogen-storage container which demonstrates a high hydrogen-storage capacity through use of a hydrogen-occlusion alloy, which is reduced in weight, and which is suited to be installed in an automobile or the like.
A hydrogen-storage container in accordance with one aspect of the invention is characterized by comprising a liner which is designed as an inner lining made of metal or resin, a fiber-reinforced resin layer provided outside the liner, a hydrogen-occlusion alloy which is located inside the liner and in which hydrogen is occluded, and an air gap portion which exists inside the liner and which is filled with hydrogen gas whose pressure is above a plateau equilibrium pressure of hydrogen gas inherent in the hydrogen-occlusion alloy at a temperature of a location where the hydrogen-occlusion container is installed.
According to the aforementioned aspect, the efficiency in storing hydrogen can be enhanced significantly through vigorous utilization of the air gap portion which is regarded as a useless space according to the related art, and the mass of the entire container can be inhibited to the utmost from increasing so that the container can be installed in an automobile. That is, while the liner can prevent hydrogen gas from leaking from the inside of the container, the fiber-reinforced resin layer can reinforce the container such that the container develops a resistance to high-pressure gas sealed therein, without increasing the weight or volume of the container.
Further, a heat exchanger and a heat-buffering substance disclosed in Japanese Patent Application Laid-Open No. 10-194701 exist in the liner. The heat-buffering substance has a melting point ranging from −10° C. to 100° C. and is selected, for example, from a group consisting of water, cyclohexane, benzene, p-xylene, biphenyl, diphenylmethane, and triphenylmethane.
According to this aspect of the invention, the container is resistant to high pressures, which leads to a decrease in heat conductivity of walls of the container. Even in the case where heat exchange from the outside of the container is difficult, the required amount of heat to be supplied to or removed from a system during occlusion or discharge of hydrogen can be reduced at least either by carrying out heat exchange required for occlusion or discharge of hydrogen by means of the heat exchanger in the container, or by utilizing latent heat while generation of heat resulting from occlusion of hydrogen causes fusion of the heat-buffering substance or while absorption of heat resulting from discharge of hydrogen causes coagulation of the heat-buffering substance.
Furthermore, the pressure of hydrogen with which the air gap portion is filled ranges from 25 MPa to 50 MPa. Thus, a hydrogen-storage container that can be filled with compressed hydrogen whose pressure is within the above-mentioned range is not heavy in particular and is therefore suited to be installed in an automobile. A larger amount of hydrogen can be stored in this hydrogen-storage container in comparison with a case where an air gap portion of a hydrogen-storage container is filled with hydrogen gas whose pressure is more or less equal to a plateau equilibrium pressure that is demonstrated by hydrogen gas contained in a hydrogen-occlusion alloy at a temperature of a location where the hydrogen-storage container is installed.
A hydrogen-storage container of the invention, which employs a hydrogen-occlusion alloy, is conceptually quite different from a previously devised hydrogen-occlusion container for storing and conveying hydrogen more or less at a normal pressure. The concept of the invention does not persist in storing hydrogen more or less at a normal pressure, and aims, as described above, at significantly enhancing hydrogen-storage efficiency through vigorous utilization of an air gap portion in a hydrogen-storage container which is regarded as useless according to the related art, and at inhibiting to the utmost an increase in the mass of the entire container so that the container can be installed in an automobile. The hydrogen-storage container of the invention has been completed as a result of extensive studies.
Although
A hydrogen-storage container 10 of the invention has a liner 20 made of metal or resin, and a fiber-reinforced resin layer 25 provided outside the liner 20. The hydrogen-storage container 10 contains a hydrogen-occlusion alloy 30, in which hydrogen is occluded. An air gap portion 40 in the container is filled with hydrogen gas (hereinafter referred to as “compressed hydrogen”) whose pressure is above a plateau equilibrium pressure of hydrogen gas contained in the hydrogen-occlusion alloy. It is to be noted herein that the liner 20 made of metal or resin is thick enough to prevent leakage of hydrogen gas from the container. For instance, for a hydrogen pressure of 25 MPa, it is appropriate that a linear made of aluminum have a thickness of 3 mm to 20 mm. The fiber-reinforced resin layer 25 is resistant to a high pressure of hydrogen gas filling the inside thereof. In addition, an inlet/outlet port 50 for hydrogen gas and a valve 60 for controlling inflow and outflow of hydrogen gas are illustrated in
Hereinafter, respective portions of the hydrogen-storage container of the invention will be described.
The hydrogen-storage container 10 of the invention has the liner 20 made from a resin or a metal such as aluminum, and the fiber-reinforced resin layer 25 provided outside the liner 20. In particular, a container having glass-fiber-reinforced resin laminated on an outer surface of a steel liner, a container having glass-fiber-reinforced resin or carbon-fiber-reinforced resin laminated on an outer surface of an aluminum liner, a container having a carbon-fiber-reinforced resin layer laminated on an outer surface of a resin liner layer, or a container having carbon fiber and glass-fiber-reinforced resin laminated on an outer surface of a resin liner is preferable because of its superiority in strength and safety. It is appropriate that these hydrogen-storage containers be cylindrical in shape.
Any hydrogen-occlusion alloy can be used as the hydrogen-occlusion alloy 30 held in the hydrogen-storage container 10. It is preferable, however, to use at least one alloy of a type that is selected, for example, from a lanthanum-nickel type, a misch metal-nickel type, a lanthanum-nickel-aluminum type, a misch metal-nickel-aluminum type, a misch metal-nickel-aluminum-cobalt type, a misch metal-nickel-aluminum-manganese type, a misch metal-nickel-manganese-aluminum-cobalt type, a calcium-nickel-misch metal-aluminum type, a titanium-iron type, a titanium-iron-manganese type, an iron-titanium-iron oxide-titanium oxide type, a titanium-iron-nickel-vanadium type, a titanium-iron-nickel-zirconium type, a titanium-cobalt type, a titanium-cobalt-iron-zirconium type, a titanium-nickel type, a titanium-manganese type, a titanium-chromium type, a titanium-zirconium-chromium-manganese type, a titanium-chromium-manganese type, a zirconium-titanium-iron-vanadium-chromium type, a magnesium-nickel type, a zirconium-manganese type, a zirconium-vanadium type, a zirconium-iron type, a calcium-nickel type, a titanium-chromium-vanadium type, and a titanium-chromium-vanadium-nickel type. Furthermore, it is possible to use hydrogen-occlusion alloy powder in which ultrafine particles of various metals are dispersed in an Mg matrix disclosed in Japanese Patent Application Laid-Open No. 2002-53926. It is especially preferable that the hydrogen-occlusion alloy employed in the invention have a plateau region at a temperature of 0° C. to 80° C. In particular, it is preferable to use at least one hydrogen-occlusion alloy of a type that is selected from a lanthanum-nickel type, a misch metal-nickel type, a titanium-chromium-manganese type, a titanium-chromium-vanadium type, and a titanium-chromium-vanadium-nickel type.
A hydrogen-occlusion alloy of any shape can be used for the hydrogen-storage container 10 of the invention. However, the use of powder is especially preferred because of its capability to enlarge a surface area of the hydrogen-occlusion alloy and to increase a rate at which hydrogen is occluded or discharged. Further, it is known that even though a hydrogen-occlusion alloy is a lump of a certain size at the outset, it gradually turns into powder due to expansion or contraction resulting from occlusion or discharge of hydrogen.
It is preferable that a hydrogen-occlusion alloy be contained in the hydrogen-storage container 10 of the invention such that a ratio (hereinafter referred to as an “air gap ratio”) of a volume of the air gap portion 40 to an internal volume ranges from 60% to 40% when no hydrogen is occluded. If the air gap ratio is further reduced, the hydrogen-occlusion alloy expands by occluding hydrogen. Thus, a high pressure may be applied to some parts of the hydrogen-storage container. On the other hand, a further increase in the air gap ratio is not preferred because the amount of storable hydrogen is reduced.
In the case where hydrogen is stored in the hydrogen-storage container 10, hydrogen is occluded into the hydrogen-occlusion alloy 30 contained in the hydrogen-storage container by filling the inside thereof with hydrogen gas. For occlusion of hydrogen, it is preferable to use compressed hydrogen. It is preferable that compressed hydrogen to be introduced into the hydrogen-storage container during occlusion of hydrogen according to the invention be at a pressure equal to or higher than 25 MPa. By introducing compressed hydrogen into the hydrogen-storage container, hydrogen can be occluded into the hydrogen-occlusion alloy at a much faster rate in comparison with a case where occlusion of hydrogen is carried out using hydrogen gas whose pressure is more or less equal to a plateau equilibrium pressure of the hydrogen-occlusion alloy during occlusion of hydrogen.
According to the invention, while hydrogen is occluded into the hydrogen-occlusion alloy 30 contained in the hydrogen-storage container, the air gap portion 40 in the hydrogen-storage container is filled with compressed hydrogen. According to the related art, the hydrogen-storage container holding the hydrogen-occlusion alloy is prevented from being filled with hydrogen gas whose pressure is equal to or higher than 1 MPa. In the hydrogen-storage container of the invention, however, it is preferable that the pressure of compressed hydrogen with which the container is to be filled range from 1 MPa to 70 MPa, especially, from 25 MPa to 50 MPa. A hydrogen-storage container that can be filled with compressed hydrogen whose pressure is within the above-mentioned range is not heavy in particular and is therefore suited to be installed in an automobile. A larger amount of hydrogen can be stored in this hydrogen-storage container in comparison with a case where an air gap portion of a hydrogen-storage container is filled with hydrogen gas whose pressure is more or less equal to a plateau equilibrium pressure that is demonstrated by hydrogen gas contained in a hydrogen-occlusion alloy at a temperature of a location where the hydrogen-storage container is installed.
A hydrogen-occlusion alloy generates heat when occluding hydrogen, and absorbs heat when discharging hydrogen. In general, therefore, means for preventing a hydrogen-storage container from being excessively heated by heat that is generated by the hydrogen-occlusion alloy during occlusion of hydrogen and for preventing a fall in hydrogen-discharge rate from being caused by absorption of heat during discharge of heat are required. Such means include the, use of a heat exchanger, a method of filling the inside of a hydrogen-storage container with a heat-buffering substance disclosed in Japanese Patent Application Laid-Open No. 10-194701, and the like. It is preferable that a heat exchanger be attached to the hydrogen-storage container of the invention. It is especially preferable that a heat exchanger be provided in the hydrogen-storage container.
Moreover, the hydrogen-storage container 10 of the invention requires components and the like for ensuring safety or the like in addition to components for filling the hydrogen-storage container with hydrogen gas and taking hydrogen out therefrom, such as a valve, a joint, and the like. If necessary, it is possible to adopt known technologies that have for long been applied to hydrogen-storage containers, high-pressure gas cylinders, and the like.
A hydrogen-storage container has been constructed by filling a pressure-resistant container having an internal volume of 1.2 L with 2.88 kg of a misch-metal-type hydrogen-occlusion alloy having a true density of 6 g/cm3, a bulk density of 2.4 g/cm3, and a hydrogen-occlusion capacity of 1 mass percent at a temperature of 25° C. Calculations based on the true density of the hydrogen-occlusion alloy used herein indicate that the inside of the container has an occupied volume of 0.48 L, that an air gap portion in the container has a volume of 0.72 L, and that the air gap occupies 60% of the container.
At a normal temperature, hydrogen gas has been introduced into the above-mentioned hydrogen-storage container, and hydrogen has been occluded into the hydrogen-occlusion alloy. After the completion of occlusion of hydrogen, the hydrogen-storage container has been filled with additional hydrogen gas which is at a pressure of 50 MPa.
After the hydrogen-storage container has been filled with additional hydrogen gas at the pressure of 50 MPa, the amount of hydrogen stored in the hydrogen-storage container is 1.94 times as large as the amount of hydrogen that is stored in the hydrogen-storage container when the air gap portion in the container has a hydrogen pressure of 0.3 MPa, namely, a plateau equilibrium pressure for hydrogen gas contained in the hydrogen-occlusion alloy in which hydrogen has been occluded.
Further, as for the hydrogen-storage container made of aluminum according to the related art and the hydrogen-storage container made of fiber-reinforced resin (FRP) according to the invention, a mass and a volume of the container required for storage of 1 kg of hydrogen have been simulated against an internal pressure of the hydrogen-storage container. This simulation is carried out on the following conditions:
The result of this simulation is illustrated in
In a hydrogen-storage container holding a hydrogen-occlusion alloy in which hydrogen is occluded, an air gap portion in the container is filled with compressive hydrogen, whereby it becomes possible to store a large amount of hydrogen in addition to occlusion of hydrogen by the hydrogen-occlusion alloy. Furthermore, the hydrogen-storage container of the invention ensures an increased storage amount of hydrogen by utilizing the air gap portion formed therein. Therefore, in comparison with a method of increasing a storage amount of hydrogen by increasing an amount of the hydrogen-occlusion alloy, the storage amount of hydrogen can be increased significantly while the mass of the container is hardly increased. As a result, the hydrogen-storage container of the invention is also suited to be installed in an automobile, whose components must be reduced in weight as a prime requirement.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-145079 | May 2003 | JP | national |
| 2002-212987 | Jul 2002 | JP | national |
